The present invention relates to a method for regenerating a tin or tin alloy plating plate.
Plating using a tin-lead alloy plating bath is effective in improving the solderability of electric component terminals and printed circuit boards, and for this reason the demand for such plating bath is increasing.
Particularly, as such tin or tin alloy plating bath, an organic acid based bath using an alkanesulfonic acid or an alkanolsulfonic acid, or a fluoroborate based plating bath using fluoroboric acid, with a bath-soluble tin salt or a tin salt and lead salt added therein and with an assistant such as a surfactant also added therein as necessary, has recently been utilized frequently for the purpose mentioned above. However, if this tin-lead alloy plating bath is used in a continuous operation over several months, the stannous ions contained in the bath will be gradually converted into stannic oxide hydrate or stannic hydroxide by reacting with oxygen in the air, by an electrode reaction or by the catalytic reaction of copper or iron ions.
Such stannic oxide and hydroxide dissolves only a little in the bath and are gradually precipitated into the bath as sludge including insoluble organic matter contained in the bath. The sludge gives rise to problems in operation such as lowering of the tin efficiency in the electrode reaction, electrodeposition of a bump-like matter, the necessity of continuous filtration for sludge disposal from the plating bath, and increase of the bath replacement frequency.
For the purpose of suppressing the formation of sludge, various methods have been adopted such as, for example, making the organic acid concentration high, reducing the plating bath temperature, decreasing the iron or copper ion concentration, removing the precipitate by continuous filtration, and the removal of sludge using only a polymeric flocculant. However, a limit is encountered in the effect obtained by these methods.
The present invention has been accomplished in view of the above-mentioned problems and it is the object of the invention to provide a method of regenerating a plating solution by the removal of sludge in an electroplating bath which is for obtaining excellent tin plating, i.e. tin plating and tin alloy plating.